This invention relates to an apparatus for detecting the passage of film-formed or sheet-formed articles, or more specifically, to an apparatus of the above-described type which is specifically utilized, for example, for the detection of the passage of a transparent copy sheet to be transported along the predetermined copy processing route within the electrophotographic copying apparatus.
Conventionally, as far as the copying process with the electrophotographic copying apparatus is concerned, the presence or absence of the copy sheet fed into the apparatus is to be detected in and around the transfer station constituting the apparatus from a standpoint of either the over-all control of the copying process or the detection of the occurrence of the jamming condition of the copy sheet in the course of the copying process.
However, according to the recent trend of the copying process with the electrophotographic copying apparatus, in addition to the employment of ordinary white paper, transparent films, which have been employed in the fields requiring the employment of the over-head projector, have come to be utilized for the above-mentioned purposes as the copy sheet. Therefore, under the circumstances as described above, the conventional sensors or detectors are no longer effective for the above-mentioned purpose due to disadvantages inherent therein.
More specifically, as for the examples of the conventional sensors or detectors, there are shown two typical arrangements in FIGS. 1 and 2, respectively. According to the conventional type as shown in FIG. 1, a microswitch 5 is positioned adjacent to a path 4 of a copy sheet 3 in a manner such that an actuator 6 of the microswitch 5 is to be spaced in the path 4 of the copy sheet 3, while the path 4 itself is arranged to be constituted by two pairs of copy sheet transporting rollers denoted by the numerals 1 and 2, respectively. On the other hand, according to another type as shown in FIG. 2, the arrangement comprises a light source 7, and its photoresponsive element 8, which are spaced with respect to each other while positioned adjacent the path 4 of the copy sheet 3 passing therebetween. Judging from the features of the arrangements as shown in FIGS. 1 and 2, it is clear that the former arrangement shown in FIG. 1 is capable of being utilized for detection of the passage of the copy sheet, irrespective of the transparency of copy sheet, but the above-mentioned arrangement is only effectively adaptable either for the case employing the copy sheet having a quality stiff enough to actuate the actuator, or for the case employing the microswitch provided with the actuator specifically having a high response characteristics as for the constituent of the arrangement mentioned above. On the contrary to the former arrangement described above, although the employment of the latter arrangement as shown in FIG. 2 is not limited to the copy process wherein the copy sheet to be employed has to be provided with the above-mentioned quality, the arrangement mentioned above is no longer employed for the copying process employing the transparent film of the above-described type as the copy sheet, which does not substantially interrupt the light beam from the light source at all. Such being the case as just mentioned above, if the arrangement is so arranged that the angle of incidence of the light beam from the light source is adjustable subject to the respective specific light transmittance and/or refractive index of the transparent film to be passed through the path mentioned earlier, the latter arrangement may be still adaptable even for the detection of the transparent film. However, the improvement added to the arrangement mentioned above will turn out not to be effective for detection, if the films to be detected are inherently provided with curl, and thereby, the predetermined fidelity in functioning of the photoresponsive element is no longer expected. Furthermore, there is another defect that the relative adjustment with respect to the spaced relationship between the light source and its photoresponsive element becomes difficult in accordance with the decrease of the angle of incidence of the light beam from the light source, which is to be predetermined for detection according to the arrangement described above.